Oxidative coupling of methane over BaCl2-TiO2-SnO2 catalyst

The performance of BaCl2-TiO2-SnO2 composite catalysts in oxidative coupling of methane reaction has been investigated. A series of BaCl2-TiO2, BaCl2-SnO2, TiO2-SnO2, and BaCl2-TiO2-SnO2 catalysts were prepared, and characterized by BET, XRD, XPS, CO2-TPD and H2-TPR, respectively. The synergistic effect among BaCl2, SnO2 and TiO2 compositions enhances the catalytic performance. The best C2 selectivity and ethylene yield are obtained on the catalyst with the equal molar amount of the three compositions (BaCl2 : TiO2 : SnO2 molar ratio of 1 : 1 : 1). The optimal reaction conditions are as follows: 800°C, 44 mL·min-1 for methane, 22 mL·min-1 for oxygen and a space velocity of 5000 mL·h-1 g-1, and the C2H4 yield over the catalyst is 20.1% with the CH4 conversion of 43.8% and C2 selectivity of 53.3%.     

Oxidative coupling of methane over Na-Mn-W/SiO2 catalyst at higher pressure

Na-Mn-W/SiO₂ catalysts were prepared and their catalytic performance for oxidative coupling of methane (OCM) was evaluated in a stainless-steel microreactor at elevated pressure. The results show that a CH₄ conversion of 15.1% with a C₂₊ selectivity of 71.8% was obtained under 750^oC, 1.0×10⁵h^-1 GHSV, CH₄/O₂ ratio of 8 and 1.0 MPa. Moreover, 17.3% CH₄ conversion with 51.6% C₂ selectivity and 23.6% C₃-C₄ selectivity was obtained under 750^oC, 2.0×10⁵h^-1 GHSV, CH₄/O₂ ratio of 8 and 1.0 MPa.     

Microwave effects on the oxidative coupling of methane over Bi2O3-WO3 oxygen ion conductive oxides

The oxidative coupling of methane over (Bi₂O₃)_1-x(WO₃)_x (x=0.2, 0.3, 0.4) oxygen ion conductive oxide catalysts irradiated by microwave has been studied. Compared with a conventional heating mode, the temperature of the catalytic bed is much lower with microwave irradiation and there is a change in selectivity favoring the production of C₂ products.     

LiCl对Fe_2O_3/SiO_2甲烷氧化偶联反应的助催化作用

使用穆斯堡尔谱，ESR和XRD等技术表征了未添加助剂和添加LiCl的Fe2O3／SiO2催化剂．XRD结果指出，添加LiCl的Fe2O／SiO2催化剂出现铁酸盐和α-方石英的衍射峰，这种结果的出现与该催化剂有较高的C2烃选择性密切相关。穆斯堡尔谱结果表明：添加LiCl的Fe2O3／SiO2催化剂有更高的结构对称性．这种结构对分子氧的活化起着重要的作用．氯的存在大大降低了氧的离解吸附的速率，减少了原子氧的吸附位的数目，并可除去吸附的原子氧，该氧种对COx的生成有利．     

LiMn_2O_4/TiO_2催化剂上甲烷氧化偶联反应性能的研究

采用固相反应法制备了具有尖晶石结构的LiMn_2O_4/TiO_2系列催化剂,探讨了TiO_2、Li/TiO_2、Mn/TiO_2、LiMn_2O_4及LiMn_2O_4/TiO_2等不同组成催化剂的甲烷氧化偶联反应性能,采用XRD、XPS、CO_2-TPD和H_2-TPR等表征方法对该系列催化剂进行了分析。结果表明,具有尖晶石结构的LiMn_2O_4化合物具有较高的甲烷氧化偶联催化活性,在775℃、0.1MPa、7200mL/(h·g),CH_4∶O_2(体积比)为2.5的条件下,甲烷转化率可达25.8%,C2选择性可达43.2%。TiO_2的存在不仅进一步提高了甲烷转化率和C2选择性,还有效抑制了甲烷完全氧化形成CO_2的过程。负载8%LiMn_2O_4的LiMn_2O_4/TiO_2催化剂性能达到最优,此时甲烷转化率达到31.6%,C2选择性为52.4%,CO_2选择性降低到26.3%。考察了不同焙烧温度对催化剂活性的影响,850℃为LiMn_2O_4/TiO_2催化剂的最佳焙烧温度。     

Mechanistic studies of methane partial oxidation to syngas over LiNiLaOx/Al2O3 catalyst

Reduction of vanadium-titanium oxide catalysts with hydrogen in the temperature range of 150–450°C results in the increase of the content of V⁴⁺ ions in substitution positions of TiO₂ with the anatase structure. The temperature increase up to 250°C results in the growth of the spectral intensity of V⁴⁺ associates in substitution positions of anatase. At higher treatment temperatures their intensity decreases due to the formation of VO₂ fragments in anatase. At 400°C and higher temperatures a solid solution of V⁴⁺ ions in rutile is formed.     

Conductivity properties of Na2SO4/CaCO3 catalysts and their effect on catalytic activities for oxidative coupling of methane

A series of Na₂SO₄ doped CaCO₃ catalysts were prepared. It was observed that the C₂ yields and selectivities of Na₂SO₄/CaCO₃ catalysts for OCM are intimately related to their conductivities. The effect of conductivity on the catalytic activity is discussed together with the conductivities and catalytic activities of the catalysts. The higher the conductivities, the higher the C₂ yields and selectivities are.     

WO3/g-C3N4异质结催化剂的制备及其氧化脱硫性能

以尿素和钨酸铵为原料采用浸渍法制备了金属氧化物三氧化钨（WO₃）与石墨相氮化碳（g-C₃N₄）异质结复合材料WO₃/g-C₃N₄。采用XRD、UV-vis、SEM、PL和XPS表征手段考察了催化剂的理化性质,发现WO₃与g-C₃N₄存在较好的相互作用和电子转移,保证了WO₃/g-C₃N₄本身所具有较高的氧化脱硫活性。以WO₃/g-C₃N₄作为催化剂,过氧化氢异丙苯为氧化剂,考察其光催化氧化脱硫性能,在反应温度80℃,O/S物质的量比为3.0的反应条件下,反应180 min,二苯并噻吩（DBT）转化率可以达到72.79%。通过游离基捕获实验,发现超氧自由基（·O₂^-）、电子（e^-）、羟基自由基（·OH）起到了促进反应速率的作用,并对该体系的反应机理进行了探讨。     

Partial oxidation of methane to syngas over Ni-Fe/Al2O3 catalyst with plasma enhanced activity

A novel Ni-Fe/Al₂O₃ catalyst for partial oxidation of methane has been prepared by glow discharge treatment followed by calcination thermally. The catalyst prepared exhibits better activity and selectivity. This revised version was published online in June 2006 with corrections to the Cover Date.     

Catalytic oxidation of methane over Pd/Co3O4

The catalytic activity of Pd/Co₃O₄ toward methane oxidation has been examined in this study as a function of Pd loading, reaction temperature, space velocity and methane concentration in the reaction gas mixture. The bare oxide is quite active achieving a 100% methane conversion at 480°C under the reaction conditions used. The catalyst with the highest Pd loading tested of 10 wt.% yields the best activity curve, but the 5 wt.% Pd/Co₃O₄ catalyst performs nearly as well. Complete conversion for this catalyst is attained at 300°C and the activity remains stable over a 90-min test period.     

Effects of operating parameters on oxidative coupling of methane over Na-W-Mn/SiO2 catalyst at elevated pressures

The effects of operating parameters on oxidative coupling of methane (OCM) over Na-W-Mn/SiO2 catalyst have been studied at elevated pressures of 0.2, 0.3 and 0.4 MPa under low gaseous hourly space velocity (GHSV) and low temperature conditions. Experimental results show that when the operating pressure is increased, C2+ yield slightly decreases, while the maximum ratio of ethylene to ethane remains unchanged. Moreover, it has been found empirically that increase of pressure does not affect the catalyst behavior permanently, the catalyst recovers its original low pressure performance without hysteresis behavior by reducing the pressure. Under the investigated conditions, when oxygen is completely consumed, the increase of GHSV leads to improvement in C2 selectivity, while C3+ and COx selectivities decrease slightly. The C2+ selectivity increases by increase of nitrogen diluent in the feed, but the C3+ hydrocarbons selectivities decrease with increase of nitrogen since it is possible that further dilution at high pressure may reduce the probability of collision between CH3 and C2+ hydrocarbons. During the stability test at high pressure, the catalyst performance remains unchanged throughout the 20 h running. The fresh and used catalysts were characterized using XRD, SEM and N2 adsorption-desorption methods. It was found that the phase transformation of the support from α-cristobalite to tridymite and quartz does not have obvious effect on catalyst performance at high pressure.     

锶掺杂对氧化镧催化甲烷氧化偶联反应的影响

甲烷氧化偶联反应(OCM)是天然气直接转化利用的重要途径之一.该反应通过甲烷和氧气在催化剂作用下一步将甲烷直接转化为乙烯等具有高附加值的产品,避免了涉及高能耗过程的合成气间接路径,不仅有可能减少中间副产物的生成,还有可能大大提升整个过程的能源利用效率.因此,研究OCM反应具有十分重要的实际意义.目前氧化镧基催化剂具有良好的催化活性、产物选择性和热稳定性,但在OCM反应中产品收率仍未能达到工业应用的要求,因而近几十年来高效OCM催化剂的研发一直是研究热点.实验发现,锶掺杂氧化镧催化剂具有更为优异的催化性能,主要表现在具有比纯氧化镧催化剂更高的催化活性和产物选择性,但对于锶掺杂的影响机制仍然缺乏系统的理论研究.目前普遍认为,甲烷活化是OCM反应的第一步,也是决速步,这主要是由于C?H键活化需要越过很高的能垒,因此往往需要很高的温度.本文主要采用团簇模型,通过密度泛函理论计算来研究OCM反应中锶掺杂对氧化镧催化剂上甲烷活化性能的影响及其作用原理.本文构建了八种锶掺杂的氧化镧团簇作为该催化剂模型,可分为没有自由基性质的团簇(LaSrO2(OH),La2SrO4,La3SrO5(OH),La5SrO8(OH))和具有自由基性质的团簇(LaSrO3,La2SrO4(OH),La3SrO6,La5SrO9).我们计算了甲烷在这些锶掺杂氧化镧团簇上Sr?O和La?O酸碱对位点以及氧自由基活性位点上的活化机制,以研究锶掺杂对OCM反应活性的影响,并与我们前期计算的纯氧化镧团簇上甲烷活化性能进行了对比.通过计算甲烷在不同锶掺杂氧化镧团簇上的物理和化学吸附能、活化能垒以及甲基自由基的脱附能,发现锶掺杂氧化镧团簇上的甲烷活化在热力学和动力学上都要比纯氧化镧团簇上更为有利.对于具有相同金属原子数目的团簇,甲烷在La?O上活化的能垒大小为:化学计量比的La?Sr?O团簇<非化学计量比的La?Sr?O团簇<化学计量比的La?O团簇;而甲烷在Sr?O上活化的能垒大小依次是:化学计量比的La?Sr?O团簇<非化学计量比的La?Sr?O团簇.给定一个锶掺杂氧化镧团簇,甲烷在不同活化位点上的活化能垒大小通常是:O·<相似文献   

Kinetics of oxidative dehydrogenation of isobutyraldehyde over Cs2HPMo12O40 catalyst

The kinetics of oxidative gas-phase dehydrogenation of isobutyraldehyde over Cs₂HPMo₁₂O₄₀ catalyst has been studied in a flow-through integral reactor at 523 K at atmospheric pressure. The catalytic reaction has been found to be accompanied by oxidation of isobutyraldehyde outside the catalyst bed. The rate of formation of methacrolein is satisfactorily described by the rate equation derived on presumption of change in the mean activation energy. The rate of the reaction in the homogeneous phase was described by empirical pseudo-first order equation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Isomerization and secondary metathesis of 2-butenes over a MoO3/Al2O3 catalyst

Transformation of cis- and trans-2-butene at 40°C was investigated over a MoO₃/A₂O₃ catalyst reduced with hydrogen and subjected to different pretreatments. Isomerization is accelerated by hydrogen preadsorbed either at low or high temperatures. The cometathesis of 2-butenes with the 1-butene intermediate, however, is enhanced only by hydrogen preadsorbed at low and suppressed by hydrogen adsorbed at high temperatures.

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- -2- 40°C MoO₃/Al₂O₃, . , , . 2- 1- , ; , .

     

Kinetic studies of the oxidative coupling of methane over the Mn/Na2WO4/SiO2 catalyst

Oxidative coupling of methane is a direct way to obtain C2 hydrocarbon,and Mn-Na-W/SiO2 catalyst is the most promising among all the catalysts.The 2%Mn/5%Na2WO4/SiO2 catalyst was prepared by the incipient wetness impregnation method.A 7-step heterogeneous reaction model of the oxidative coupling of methane to C2 hydrocarbons was conducted by co-feeding methane and oxygen at a total pressure of 1 bar over the catalyst.The kinetic measurements were carried out in a micro-catalytic fixed bed reactor.The kinetic data were obtained at the appropriate range of reaction conditions (4 kPa＜Po2 ＜20 kPa,20 kPa＜PCZH4 ＜80 kPa,800℃＜T＜900℃).The proposed reaction kinetic scheme consists of three primary and four consecutive reaction steps.The conversions of hydrocarbons and carbon oxides were evaluated by applying Langrnuir-Hinshelwood type rate equations.Power-law rate equation was applied only for the water-gas shift reaction.In addition,the effects of operating conditions on the reaction rate were studied.The proposed kinetic model can predict the conversion of methane and oxygen as well as the yield of C2 hydrocarbons and carbon oxides with an average accuracy of ±15%.     

Peculiarities in oxidative conversion of methane to C2 hydrocarbons over CaO?CaCl2 catalysts

Experimental data for the oxidative dimerization of methane over CaO–CaCl₂ systems indicate that C₂ hydrocarbons are formed with the participation of chlorine generated by the catalyst surface under the effect of a reaction medium. A heterogeneous-homogeneous scheme for this process is suggested.

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CaO–CaCl₂ , C₂- , . - .

     

Product oriented oxidative bromination of methane over Rh/SiO2 catalysts

Rh/SiO2 was prepared for the oxidative bromination of methane. The catalyst was prepared by calcination at different temperatures and for different times to obtain catalysts with different specific surface areas for the purposes of producing either CH3Br or CH3Br and CO. It was found that the catalyst having a low specific surface area (calcined at relatively high temperature) favors the selective oxidation of methane to prepare CH3Br, while the catalyst having a high specific surface area favors the deeper partial oxidation of methane, which is good for CH3Br and CO preparation. The 650 h on stream life-time test revealed that the catalytic performance of the 0.4Rh/SiO2--900-10 catalyst was excellent. Both methane conversion and CH3Br selectivity kept increasing trends during the life-time test. No matter how serious was the Rh leaching during the reaction, the 0.4Rh/SiO2--900-10 catalyst did not deactivate at all.     

LaCoO3对H2S选择氧化性能的影响

使用溶胶-凝胶法制备了LaCoO₃催化剂,采用XRD、BET和XPS等方式对催化剂进行了表征,考察了该催化剂制备过程中煅烧温度、表面活性剂PEG-6000和PEG-20000含量对其H₂S选择氧化制硫磺反应催化活性的影响。结果表明,表面活性剂PEG-6000及PEG-20000的添加能明显提高LaCoO₃的催化活性。0.02 mol La（NO₃）₃+0.02mol Co（NO₃）₂溶液中添加0.30 g PEG-20000、煅烧温度为650℃时所制备的LaCoO₃催化活性最好;在最佳反应温度260℃下,H₂S的转化率达到96.10%,硫选择性为93.77%。